Piezoelectric device having a resistor and a plastic insulating casing

ABSTRACT

Two ceramic rods, made from a piezoelectric material are mounted end-to-end in a high impact glass-filled plastic case. The rods are precision machined to close tolerances at the ends, then silver electroded on those ends, and then polarized at high voltage to establish two poles of opposite polarity at the opposite ends of each rod. The two rods are placed in coaxial end-to-end relation, with the ends of like polarity placed in butting relation. An impact force applied at the end of one of the two rods, when thus positioned, causes a high voltage electrical current to be generated across the respective electrodes. Mechanically, the rods are compressed in series relationship by the applied mechanical impact force, each rod being stressed practically to the same value. Electrically, the rods are operating in parallel between the two outer ends of the same polarity, and the two inner ends, which are engaged through a metallic terminal tab, that serves as a terminal for the tworod assembly. This parallel arrangement of the two rods doubles the current that would be available from a single rod, and produces a hot spark. The two outer ends of the rods, as assembled, are of the same polarity and they are, preferably, connected to ground, which may be the casing in which the ignitor is disposed. The two middle ends are in contact with a center terminal tab which is connected to one end of a resistor, the other end of the resistor being provided with an electrode whose free end is disposed to define one end of a gap in space where the gaseous vapor is to be ignited to provide the flame for the lighter or other device. The resistor is designed for high voltage operation and is suitably insulated, except for the outer end of its terminal, which is otherwise suitably disposed in the lighter casing that will be inaccessible to the finger of the human hand which is operating the lighter. The discharge of current from the compressed rods is, essentially, a condenser discharge which is limited in duration only by the impedance of the discharge circuit. The provision of the resistor assures delay to permit sufficient ionization time in the vapor to establish arcing and ignition of the vapor.

United States Patent [72] Inventor Ralph K. Hellen Chicago, Ill. [21] Appl. No. 804,860 [22] Filed Mar. 6, 1969 [45] Patented June 15, 1971 [73] Assignee P. R. Mallory & Co., Inc.

Indianapolis, Ind.

[54] PIEZOELECTRIC DEVICE HAVING A RESISTCR AND A PLASTIC INSULATING CASING 2 Claims, 5 Drawing Figs.

[52] U.S. Cl 3l0/8.2, 317/81, 455/255 [51] Int. Cl H0lv 7/00 [50] Field of Search 317/81, 79,

[ 56] References Cited 7 UNITED STATES PATENTS 3,387,149 6/1968 Young 310/85 3,486,075 12/1969 Steinke et al. 317/81 3,360,665 12/1967 Boswell 3l0/8.7 3,384,786 5/1968 Oyamada et a1. 317/81X 3,425,783 2/1969 Goto 431/255 3,434,790 3/1969 Kanda 431/255 3,457,461 7/1969 Steinke et a1. 317/81 FOREIGN PATENTS 6,804,187 9/1968 Netherlands 317/81 ABSTRACT: Two ceramic rods, made from a piezoelectric material are mounted end-to-end in a high impact glass-filled plastic case. The rods are precision machined to close tolerances at the ends, then silver electroded on those ends, and then polarized at high voltage to establish two poles of opposite polarity at the opposite ends of each rod. The two rods are placed in coaxial end-to-end relation, with the ends of like polarity placed in butting relation. An impact force applied at the end of one of the two rods, when thus positioned, causes a high voltage electrical current to be generated across the respective electrodes. Mechanically, the rods are compressed in series relationship by the applied mechanical impact force, each rod being stressed practically to the same value. Electrically, the rods are operating in parallel between the two outer ends of the same polarity, and the two inner ends, which are engaged through a metallic terminal tab, that serves as a terminal for the two-rod assembly. This parallel arrangement of the two rods doubles the current that would be available from a single rod, and produces a hot spark. The two outer ends of the rods, as assembled, are of the same polarity and they are, preferably, connected to ground, which may be the casing in which the ignitor is disposed. The two middle ends are in contact with a center terminal tab which is connected to one end of a resistor, the other end of the resistor being provided with an electrode whose free end is disposed to define one end of a gap in space where the gaseous vapor is to be ignitedto provide the flame for the lighter or other device. The resistor is designed for high voltage operation and is suitably insulated, except for the outer end of its terminal, which is otherwise suitably disposed in the lighter casing that will be inaccessible to the finger of the human hand which is operating the lighter. The discharge of current from the compressed rods is, essentially, a condenser discharge which is limited in duration only by, the impedance of the discharge circuit. The provision of the resistor assures delay to permit sufficient ionization time in the vapor to establish arcing and ignition of the vapor.

' PIEZOELECTRIC DEVICE HAVING A RESISTOR AND A PLASTIC INSULATING CASING DESCRIPTION This invention relates to an ignitor element to serve as a spark source for gas-operated devices, such as torches, cigarette lighters and the like, in which the gas vapor is ignited by an electric spark as generated by a high voltage applied to two closely spaced terminals as a gap in a small region through which the gas vapor is guided. I

In the use of piezoelectric devices for generating a high voltage for sparking purposes, an impact force is necessarily of short duration, and the resulting high voltage has a waveform that has a steep rise and fall. As a result, the duration ofsuch a voltage is very short.

Ignition is not an instantaneous process, but requires a finite time, according to the applied voltage and the original' condb tion of ionization in the arc space between the electrodes If the voltage wave generated by the piezoelectric device is of short duration, sufficient ionization and movement of the ions in the arc gap may not be established by a single voltage wave or surge, and several successive operations may be necessary to generate a condition of ionization in the gap that willpermit ignition finally.

One object of the invention is to provide a piezoelectric device which will generate a high voltage when subjected to an impact force, and to provide, in association with said device, a suitable resistor to delay the transfer of energy from the piezoelectric device to an arcing terminal co'nnectedat the outer end of the resistor, in order thereby to delay the decay time of the electric field generated at the outer terminal connected to the resistor.

Another object of the invention is to provide a piezoelectric crystal device, consisting of at least two units, axially aligned in a manner to permit a single impact force to be applied thereto, to generate a high voltage from the two units, with the units connected electrically in parallel to supply a substantial relatively simple in construction, easy to fabricate'and low in cost.

These and other objects and the various advantages of the invention, and the manner in which these objects and advantages are obtained, will be explained in more detail and will be apparent to those conversant with the art from the following description and subjoined claims, taken in conjunction with the annexed drawing, in which:

FIG. 1 is a schematic diagram of a piezoelectric device of. this invention, showing two polarized rods in coaxial disposition with similar poles end-to-end, and with a delaying resistor connected to the midpoint or junction of the two rods, and having an arcing electrode connected at its outer end;

FIG. 2 is a side elevational view of the actual device, that is schematically illustrated in FIG. I, with parts broken away to show the internal disposition of the two polarized piezoelectric rods and the delaying resistor;

FIG. 3 is a schematic drawing to illustrate the equivalent force that is to be applied to the piezoelectric device of FIGS. 1 and 2 in order to generate the desired design voltage sufficient to cause an arc in a gap designed to a predetermined dimension within which the gaseous vapor will be ignited;

FIG. 4 is a graph showing the relationship to time-of an output voltage from the piezoelectric device of FIGS. 1 and 2', to illustrate the form of the voltage curve and the time of duration, in the case without a resistor, and in the case with a re,- sistor provided to enlarge the time during which the voltage is effective to ionize the spark and cause ignition; and

FIG. 5 is a schematic front view ofa structure ofa hand-carried and hand-operated lighter in which a piezoelectric device of the present invention is disposed.

As shown in FIG. 1, a piezoelectric device 10 to serve as an ignitor, in accordance with the principles of this invention, comprises two rods 12 and 14 of piezoelectric material and a resistor 16.

The two rods 12 and 14 are polarized to establish end poles of the polarities indicated at their respective ends 12A and 12B, and 14A and 148. The rods are precision machined to close tolerances in exact transverse planes at their ends to enable full surface-to-surface contact to be made for optimum average distribution of an applied external force 15. Both ends of each rod are then silver electroded for good electrical connections.

The two rods 12 and 14 are positioned coaxially, as shown, with the positive terminals in contact, and the negative terminals are electrically connected by a suitable electrical conductor 22 which is grounded at 24.

A thin electrical tab 18 between the adjacent ends 12A and 14A connects to one end of the resistor 16. The other end of resistor 16 consists of an elongated straight terminal whose outer end 25 serves as the arcing point at the gap 26 to another terminal 28 that is grounded to complete the electrical circuit for the high voltage to the ground point 24.

As shown in FIG. 2, the two rods 12 and 14 are coaxially disposed and held tightly compressed with their inner ends tightly pressed against the tab 18. The two rods 12 and 14 are held in such tight, compressed relationship by and within a casing 30, consisting of a high impact glass-filled plastic material. To permitelectrical connections to be made to the two outer electrodes 12B and 14B, two metallic impact heads 32 and 34 are provided in electrical and mechanical connection to the two outer electrodes 12B and 14B of the two rods Hand 14.

The resistor 16 is shown disposed in a compartment alongside of the space in which the rod 14 is disposed and the resistor I6 is also insulated and enclosed within a portion of the casing 30; in such manner as to be suitably insulated from the rod-l4. As shown, the upper end of the resistor is connected to the tab 18 and the lower end of the resistor has connected thereto an elongated self-supporting wire rod 20 corresponding tothat shown in FIG. 1. The rod-20 is linear and free of any bends or sharp edges that would introduce any conditions beyond the control delay designed into the unit by the provision of the resistor 16 of appropriate resistance.

In FIG. 3 is shown, schematically, the amount of impact force required for a device of the form here shown in FIGS. 1 and 2. The ball 40 represents a weight of l 1.8 grams and the distance of fall is 30 centimeters.

In FIG. 4, two graphs are shown. The inner graph 45, with sharp rise and fall, shows the form of a voltage wave generated across the two rods 12 and 14, when disposed as shown, without'a resistor interposed in the circuit from the engaging electrodes to an external arc gap. For the purpose of comparison, the peak voltage of that inner graph 45 is about 10 to l l kilovolts. The second graph50 shows the effect of the resistor 16 in widening the curve and thus, increasing the duration of the voltage wave to the arc gap, and thereby increasing the duration of the time within which an arc may form to ignite the fuel vapor to form a flame.

As a-basis of comparison, the time spacing between halfpower points of the fast curve 45, is about 10 microseconds, whereas in the slow curve 50, with resistor, the spacing is about 40 microseconds.

In FIG. 5 is shown a typical hand-type lighter, in a casing 60 containing an ignitor 10, a fuel container 70, a valve 75 between the fuel container 70and an outlet tube 77 for the fuel vapor. A closure cap 80 for the casing 60 is pivoted on a hinge 82 and operates the valve 75 to open or to closed position, correspondingtothe position of the cap 80.

An impact device 85 is disposed above the top of the ignitor l0, and comprises an insulated impact bottom mass 87, with a finger trigger 8810 raise the mass by a finger against the reaction of a compression spring 92, and then to release the mass 87 for downward movement to strike against the top head 32 of the piezoelectric device 10, the bottom head 34 being electrically and mechanically engaged against the inner surface of the bottom wall of the casing 60.

The high voltage generated across the piezoelectric device is then conducted to the end of linear conductor and the top of the vapor tube 77 to energize gap 26 and cause a spark which will ignite the fuel vapor. The resistor 16, about 27 kilohms, provides the desired delay to increase the time for the arc to form.

The invention is not limited to the form and arrangement shown as a preferred embodiment, but may be varied without departing from the spirit and scope of the invention as defined in the claims.

What I claim is:

l. A piezoelectric device useful as a spark generating ignitor comprising a pair of cylindrically shaped, axially polarized piezoelectric elements coaxially disposed with the abutting ends thereof having the same polarity, each of said elements having end faces with metal electrodes disposed thereon, a cylindrically shaped, plastic insulating casing enclosing said elements, two metallic impact heads in electrical and mechanical connection to the two outer electrodes and extending through said plastic insulating casing, a resistor disposed adjacent and parallel to said elements, said resistor insulated from said elements by said casing and enclosed within cylindrically shaped plastic casing integrally formed with said casing, an electrical lead connecting one end of said resistor to the abutting electroded faces of said elements, and an electrical lead connected to the other end of said resistor and extending through said casing to provide an external terminal.

2. A piezoelectric device according to claim 1, wherein said casing comprises a glass filled dielectric material. 

1. A piezoelectric device useful as a spark generating ignitor comprising a pair of cylindRically shaped, axially polarized piezoelectric elements coaxially disposed with the abutting ends thereof having the same polarity, each of said elements having end faces with metal electrodes disposed thereon, a cylindrically shaped, plastic insulating casing enclosing said elements, two metallic impact heads in electrical and mechanical connection to the two outer electrodes and extending through said plastic insulating casing, a resistor disposed adjacent and parallel to said elements, said resistor insulated from said elements by said casing and enclosed within cylindrically shaped plastic casing integrally formed with said casing, an electrical lead connecting one end of said resistor to the abutting electroded faces of said elements, and an electrical lead connected to the other end of said resistor and extending through said casing to provide an external terminal.
 2. A piezoelectric device according to claim 1, wherein said casing comprises a glass filled dielectric material. 